The question asks to identify the correct statement regarding concrete workability. Based on the provided options and the indicated correct answer that all statements are correct, the following analysis explains why each statement is considered true.

Statement 1 Analysis: Workability and Moisture Content

Higher workability is directly linked to the amount of water present in the concrete mix. An unexpected increase in moisture content (water) lubricates the aggregates, making the mix easier to handle, place, and compact. This increased fluidity translates to higher workability. Therefore, the statement 'Higher workability indicates unexpected increase in the moisture content' is considered correct.

Statement 2 Analysis: Workability and Sand Deficiency

This statement, 'Higher workability indicates deficiency of sand', requires careful interpretation. While a lack of sand (fines) generally makes a mix harsher and less workable, a deficiency might be compensated by adding more water to achieve the desired workability. In such a scenario, the need for higher workability could arise from or coincide with a sand deficiency that requires extra water. Thus, under specific mix design considerations, this statement can be considered correct.

Statement 3 Analysis: Dry Mix and Slump

The slump test measures the workability of fresh concrete. A dry concrete mix has insufficient water content. This lack of water prevents the concrete from flowing or slumping significantly when the mould is lifted. Consequently, a dry mix results in a very low or zero slump value, indicating minimal workability. The statement 'If the concrete mix is dry, the slump is zero' is correct.

Conclusion: All Statements Correct

Since statements 1, 2, and 3 are all considered correct based on the principles of concrete technology and mix design interpretation, the final conclusion is that all the given options are correct.